The present invention relates generally to a storage apparatus and a position sensitivity setting method, ensuring constant position sensitivities by adjusting into a predefined level the intersection level of two position signals demodulated from two-phase servo information buried and recorded in a medium, and more particularly to a storage apparatus and a position sensitivity setting method correcting nonlinear position sensitivities possessed by the position signals into linear ones.
With the recent demands for larger capacities and smaller dimensions of the magnetic disk units, the track density (TPI) becomes even higher, making improvement of the servo signal based position accuracy for realizing this more significant. As opposed to the conventional servo-surface servo needing dedicated servo surface and servo head, a more cost-effective sector servo, so-called data-surface servo ensuring increased recording capacities has been adopted in which servo information is buried in the data surface at its sector leading position. In case of recording two-phase servo information in the servo-surface servo or sector servo, two position signals N and Q having different phases by 90 degrees (xc2xd track pitch) are demodulated from servo signals read from the disk medium, and on the basis of these position signals N and Q the seeking operations by the head coarse control and the positioning operations by the fine control are carried out. The two position signals N and Q demodulated from the two-phase servo information indicate the head position by their respective signal levels, and therefore, irrespective of any variances in the read signals as a result of dispersions of the core width, the two finally demodulated position signals N and Q must always have unvarying amplitudes at the head position at the intersection level where the two coincide with each other. To this end, upon the apparatus setup for example, a position sensitivity adjustment is carried out which includes moving the head at a low speed, detecting and storing an intersection level where the two position signals N and Q coincide with each other, and setting into an AGC amplifier the gain which has the intersection level as a predefined theoretical value, to thereby keep constant the sensitivities of the two position signals N and Q relative to the head position.
FIG. 1 shows a conventional position sensitivity adjustment circuit directed to the servo-surface servo. Referring to FIG. 1, upon the position sensitivity adjustment, two position signals N and Q having 90-degrees shifted phases are demodulated from the read signal of the two-phase servo information on the servo surface with the VCM being driven at a low speed, and then amplified by AGC amplifiers 102 and 104, after which they are converted into absolute position signals |N| and |Q| by absolute value circuits 106 and 108 for the impartment to an intersection level detection circuit 110.
FIG. 2A shows the position signals N and Q output from the AGC amplifiers 102 and 104 with the axis of abscissas representative of the actual track position X. The position signals N and Q from the AGC amplifiers 102 and 104 are converted into the absolute position signals |N| and |Q| by the absolute value circuits 106 and 108. The intersection level detection circuit 110 compares the absolute value signals |N| and |Q| of FIG. 2B to detect the signal levels at the intersections 114, 116, 118, 120, etc., and stores the average value thereof as the intersection value in a storage 112. The gains of the AGC amplifiers 102 and 104 of FIG. 1 are adjusted such that the intersection value stored in the storage 112 coincides with a certain value (theoretical value). Such a position sensitivity adjustment is carried out for each head and on a disk medium zone basis, and the position signals N and Q are amplified by the AGC amplifiers 102 and 104 so that the intersection level of the position signals N and Q coincides with the certain value (theoretical value) to acquire constantly unvarying position sensitivities. This is the position sensitivity correction or the head core width correction in the state of the art, which allows adjustment for constantly unvarying position sensitivity and high-precision position detection to be made in spite of the core width dispersions on a head-to-head basis.
By the way, a higher medium track density TPI attendant on the increased capacity and reduced dimensions necessitates more precise position sensitivities. However, the position signals N and Q demodulated from the two-phase servo information shown in FIG. 2A are merely ideal signals lacking the consideration for, e.g., the leakage flux to the head cores and are regarded as having a linear characteristic that the position signals N and Q relative to the actual track position X are linear within the range below the intersection level, with the position sensitivities keeping constantly unvarying values. More strictly, however, the position signals are under the influence of the leakage flux so that the positions signals are not precisely linear relative to the actual track position X even in the range below the intersection level, thus presenting the nonlinear position sensitivities. Nevertheless, the position sensitivity is regarded as constant within the range below the intersection level to correct the intersection level to a certain level (theoretical value), i.e., to make one-point correction. This does not mean the adjustment of the nonlinear position sensitivities into constant sensitivities. Thus, there lies an error between the intersection level based one-point linear corrected position sensitivities and the actual nonlinear position sensitivities. This position sensitivity error may impede the acquisition of high-precision signals required for the higher track density TPI.
According to the present invention there are provided a storage apparatus and a position sensitivity setting method therefor, capable of acquiring high-precision position signals by further correcting nonlinear position sensitivities once corrected on the basis of the intersection of two position signals demodulated from two-phase servo information, into linear ones.
The storage apparatus of the present invention comprises a position sensitivity adjusting unit and a sensitivity correcting unit. The position sensitivity adjusting unit detects the signal level at the intersection of position signals N and Q having different phases Ø by a predetermined track pitch (TP/n), e.g., TP/2 which are demodulated from read signals of two-phase servo information buried and recorded in a disk medium, the position sensitivity adjusting unit making an adjustment of the gain of an AGC amplifier so that the intersection signal level coincides with a predetermined level. Herein, n represents any arbitrary integers including 1, 2, 3, 4, etc. The sensitivity correcting unit corrects nonlinear position sensitivities relative to the actual track position X of two position signals N and Q output from the AGC amplifier, into linear position sensitivities. In this manner, the present invention feeds by no means the position signals N and Q having nonlinear position sensitivities intactly to the control circuit, but instead creates position signals Na and Qa whose nonlinear position sensitivities have been corrected into linear position sensitivities by the correction circuit, previous to the feed to the control circuit, thereby making it possible to provide a precise head position control irrespective of the nonlinear head detection characteristics whereby a high-precision head position control can be provided especially in the event of the increased track densities of the disk medium.
Herein, the sensitivity correcting unit corrects nonlinear position sensitivities of the position signals N and Q, into linear position sensitivities having certain sensitivities at the intersection detected by the position sensitivity adjusting unit. The sensitivity correcting unit corrects nonlinear position sensitivities of the position signals N and Q into linear position sensitivities within the range of up to the track position corresponding to the intersection from the track center. The sensitivity correcting unit approximates the position sensitivities of two position signals N and Q output from the AGC amplifier by predetermined nonlinear functions to correct them into linear position sensitivities. The sensitivity correcting unit approximates two position signals N and Q relative to the actual track position X output from the AGC amplifier by sine functions
N=sin X
Q=sin (Xxe2x88x92TP/n)
the sensitivity correcting unit defining linear functions of two position signals Na and Qa which are corrected relative to the actual track position X, as
Na=X
Qa=Xxe2x88x92TP/n
to thereby obtain relational expressions of the two
N=sin Na
Q=sin Qa
Then, the sensitivity correcting unit figures out from the relational expressions the corrected position signals Na and Qa as
xe2x80x83Na=sinxe2x88x921 N
Qa=sinxe2x88x921 Q
to thereby correct nonlinear position sensitivities into linear ones.
The sensitivity correcting unit figures out the linearly corrected position signals Na and Qa from
Na={1/({square root over (2)}xc2x7cos N)}xc2x7N
Qa={1/({square root over (2)}xc2x7cos Q)}xc2x7Q
which are specific examples of expressions used for obtaining the corrected position signals Na and Qa. These expressions are obtained, in case of converting nonlinear functions into linear functions, by differentiating the nonlinear functions to find the reciprocals and multiplying the nonlinear functions by thus obtained reciprocals. That is, the expressions approximated by sine functions
N=sin Na
Q=sin Qa
are differentiated to obtain the inclinations
Nxe2x80x2=(sin Na)xe2x80x2=cos Na
Qxe2x80x2=(sin Qa)xe2x80x2=cos Qa
Then the reciprocals of the inclinations are normalized to find product coefficients
KN=1/({square root over (2)}xc2x7cos N)
KQ=1/({square root over (2)}xc2x7cos Q)
which are multiplied by the nonlinear position signals N and Q to obtain
xe2x80x83Na=KNxc2x7N={1/({square root over (2)}xc2x7cos N)}xc2x7N
Qa=KQxc2x7Q={1/({square root over (2)}xc2x7cos Q)}xc2x7Q
The sensitivity correcting unit previously prepares, in the form of table information, one of the values of product coefficients as
KN=1/({square root over (2)}xc2x7cos N)
The sensitivity correcting unit determines the product coefficients KN and KQ by reference to the table information by position signals P and Q from the AGC amplifier and multiplies the position signals P and Q by the thus determined product coefficients KN and KQ to thereby correct nonlinear position sensitivities into linear ones. In this correction using the table information, depending on the polarities of the two the sensitivity correcting unit converts the position signals N and Q into
(+, xe2x88x92); +N, +(Q+TP/n)
(+, +); +(2 TP/nxe2x88x92N), +{2 TP/nxe2x88x92(Q+TP/n)}
(xe2x88x92, +); xe2x88x92(2 TP/n+N), +{2 TP/n+(Q+TP/n)}
(xe2x88x92, xe2x88x92); xe2x88x92(4 TP/nxe2x88x92N), xe2x88x92{4 TP/nxe2x88x92(Q+TP/n)}
previous to reference to the table information. Thus, by preparing one product coefficient table about the range (xe2x88x92TP/2 nxe2x89xa6N, Qxe2x89xa6TP/2 n) up to the intersection from the track centers of the position signals N and Q, the position sensitivity linear correction can be effected within one cycle range (4 TP/n0 track pitch range) of the position signals N and Q. The sensitivity correcting unit may approximate two position signals N and Q having nonlinear position sensitivities relative to the actual track position X output from the AGC amplifier by cosine functions
N=cos X
Q=cos (Xxe2x88x92TP/2)
the sensitivity correcting unit defining two corrected position signals Na and Qa having linear position sensitivities relative to the actual track position X, as linear functions
Na=X
Qa=Xxe2x88x92TP/2
xe2x80x83to thereby obtain relational expressions of the two
N=cos Na
Q=cos Qa
xe2x80x83the sensitivity correcting unit figuring out the corrected position signals Na and Qa from the relational expressions as
Na=cosxe2x88x921 N
Qa=cosxe2x88x921 Q
xe2x80x83to thereby correct nonlinear position sensitivities into linear ones. In this case, similar to the sine functions, the sensitivity correcting unit figures out corrected position signals Na and Qa from
Na=xe2x88x92{1/({square root over (2)}xc2x7sin N)}xc2x7N
Qa=xe2x88x92{1/({square root over (2)}xc2x7sin Q)}xc2x7Q
xe2x80x83That is, the cosine function approximated relational expressions
N=cos Na
Q=cos Qa
xe2x80x83are differentiated to obtain the inclinations
Nxe2x80x2=(cos Na)xe2x80x2=xe2x88x92sin Na
Qxe2x80x2=(cos Qa)xe2x80x2=xe2x88x92sin Qa
xe2x80x83Then the reciprocals of the inclinations are normalized to obtain product coefficients
KN=xe2x88x921/({square root over (2)}xc2x7sin N)
KQ=xe2x88x921/({square root over (2)}xc2x7sin Q)
xe2x80x83which are multiplied by the nonlinear position signals N and Q to obtain
Na=KNxc2x7N=xe2x88x92{1/({square root over (2)}xc2x7sin N)}xc2x7N
Qa=KQxc2x7Q=xe2x88x92{1/({square root over (2)}xc2x7sin Q)}xc2x7Q
xe2x80x83The sensitivity correcting unit previously prepares, in the form of table information, the value of the product coefficient
KN=xe2x88x921/({square root over (2)}xc2x7sin N)
xe2x80x83for use in calculation of the corrected position signals Na and Qa. The sensitivity correcting unit determines the product coefficients KN and KQ by reference to the table information by position signals P and Q from the AGC amplifier and multiplies the position signals P and Q by the thus determined product coefficients KN and KQ to thereby correct nonlinear position sensitivities into linear ones. In this case as well, depending on the polarities of the two the sensitivity correcting unit converts the position signals N and Q into
(+, +); +(TP/nxe2x88x92N), +{TP/nxe2x88x92(Q+TP/n)}
(xe2x88x92, +); xe2x88x92(TP/n+N), +{TP/n+(Q+TP/n)}
(xe2x88x92, xe2x88x92); xe2x88x92(3 TP/nxe2x88x92N), xe2x88x92{3 TP/nxe2x88x92(Q+TP/n)}
(+, xe2x88x92); +(3 TP/n+N), xe2x88x92{3 TP/n+(Q+TP/n)}
xe2x80x83previous to reference to the table information.
Furthermore, the sensitivity correcting unit may approximate the nonlinear functions of two position signals N and Q relative to the actual track position X output from the AGC amplifier by polynomial expressions
N=ANXN+AN-1XN-1+ . . . +A0
Q=AN(Xxe2x88x92TP/n)N+AN-1(Xxe2x88x92TP/n)N-1+ . . . +A0
the sensitivity correcting unit defining linear functions of two corrected position signals Na and Qa relative to the actual track position, as
Na=X
Qa=Xxe2x88x92TP/n
xe2x80x83to thereby obtain relational expressions of the two
N=ANNaN+AN-1NaN-1+ . . . +A0
Q=ANQaN+AN-1QaN-1+ . . . +A0
xe2x80x83to thereby correct nonlinear position sensitivities into linear ones.
The present invention further provides a position sensitivity setting method for a storage apparatus, comprising a position sensitivity adjustment step which includes detecting the signal level at the intersection of position signals N and Q having different phases Ø by a predetermined track pitch (TP/n) which are demodulated from read signals of two-phase servo information buried and recorded in a disk medium, the position sensitivity adjustment step including making an adjustment of the gain of an AGC amplifier so that the intersection signal level coincides with a predetermined level; and a sensitivity correcting step which includes correcting nonlinear position sensitivities relative to the actual track position X of two position signals N and Q output from the AGC amplifier, into linear position sensitivities.